Hydroxyl Changing Mechanism of Cotton Cellulose during Alkaline Treatment Characterized by ATR-FTIR in Combination with Two-Dimensional Correlation Spectroscopy

Hydroxyl changes of cotton cellulose treated with sodium hydroxide (NaOH) solution is closely related with hydrogen bonding (H-bonds) between different hydroxyls, which is difficult to directly measure by common instrumentational methods of X-ray diffraction (XRD) or Fourier transform infrared (FTIR) spectroscopy. Two-dimensional correlation spectroscopy (2Dcos) is a powerful tool to analyze the changes of molecular spectroscopy. In this study, the alkaline- treated cotton cellulose was monitored in real time by attenuated total reflection (ATR) in combination with 2Dcos. Results indicated that the H-bonds changed in the following sequence order: ν(O3-H3...O5) (intramolecular) → ν(O6-H6...O3') (intermolecular) → ν(O2-H2...O6) (intramolecular). Moreover, Gaussian computational modeling analysis also confirmed this mechanism. Both XRD and FTIR results indicated the decrease of crystallinity of the alkaline-treated cotton cellulose over prolonged time.